Two of three defendants charged with kidnapping a man for ransom and assaulting him in 2007 have pleaded guilty to kidnapping charges in Sonoma County Superior Court.Boonlak Phanchanh, 23, pleaded guilty today to kidnapping and to an enhancement alleging the crime was gang related. He faces a 13-year prison term when he is sentenced June 9, his attorney Walter Rubenstein said. Pongsony Patrick Khaoone, 29, pleaded guilty to kidnapping and to the gang enhancement Friday in return for a 15-year prison sentence. He will be sentenced May 24.Robbery, burglary and other charges against the men will be dismissed at sentencing.A third defendant, Perry Phongaun Khaoone, 25, will be tried on 11 felony charges April 28. All three were charged with kidnapping Terry Au, 24, from his Santa Rosa home on Oct. 1, 2007. Santa Rosa police said the three men beat Au, strangled him with a chord, burned him in the face with a cigarette and threatened to cut off his fingers.Au testified at a hearing he was kidnapped and beaten because he did not want to provide drugs for the Khaoones.Au’s brother Vutha Au, 24, was kidnapped and killed March 2, 2008, at Blind Beach on the Sonoma Coast. Vutha Au had agreed to testify against the three kidnapping-for-ransom defendants, the Sonoma County District Attorney’s Office said.Five men, including Preston Phongsuvane Khaoone, 24, the Khaoones’ brother, have been charged with Vutha Au’s murder and with killing a witness to prevent his testimony. All are alleged Asian Boyz gang members. Their trial is pending.The other murder defendants are Tyrone Tay, a Solano County resident; David Prak, 21, and his brother Sarith Prak, 23, and Quentin Russell, 26, all of Santa Rosa.Au was shot nine times in the head, neck and torso. His body was found in a parking lot by a state parks ranger.He had been placed in the California Witness Relocation and Assistance Program in anticipation of his testimony at the kidnapping-for-ransom trial but he returned to the Santa Rosa area.